This invention is related to a high-pressure, common rail, fuel injection system for injecting metered amounts of highly pressurized fuel into the cylinder of a diesel engine.
Conventional fuel injection systems employ a "jerk" type fuel system for pressurizing and injecting fuel into the cylinder of a diesel engine. A pumping element is actuated by an engine-driven cam to pressurize fuel to a sufficiently high pressure to unseat a pressure-actuated injection valve in the fuel injection nozzle. In one form of such a fuel system having an electromagnetic unit injector, the plunger is actuated by an engine driven cam to pressurize the fuel inside the bushing chamber when a solenoid is energized and the solenoid valve is closed. The metering and timing is achieved by a signal from an electronic control module (ECM) having a controlled beginning and a controlled pulse. In another form of such a fuel system, the fuel is pressurized by an electronic or mechanical pumping assembly into a common rail and distributed to electromagnetic nozzles, which inject pressurized fuel into the engine cylinders. Both the electronic pump and the electromagnetic nozzles are controlled by the ECM signal.
One problem with using a common rail results from the high pressures experienced in diesel engines, which are in the neighborhood of 20,000 psi. Another problem in conventional fuel injection systems is achieving a controlled duration and cut-off of the fuel injection pressure. Standard fuel injection systems commonly have an injection pressure versus time curve in which the pressure increases to a maximum and then decreases, following a somewhat skewed, triangularly-shaped curve. Such pressure versus time relationship initially delivers a relatively poor, atomized fuel penetration into the engine cylinder because of the low injection pressure. When the pressure curve reaches a certain level, the pressure provides good atomization and good penetration. As the pressure is reduced from its peak pressure, the decreasing pressure again provides poor atomization and penetration, and the engine discharges high emissions of particulates and smoke.
One of the objects of fuel injection designers is to reduce unburned fuel by providing a pressure versus time curve having a square configuration, with an initially high pressure increase to an optimum pressure, providing good atomization, and a final sharp drop to reduce the duration of poor atomization and poor penetration.
Examples of some prior art fuel injection nozzles may be found in U.S. Pat. No. 4,527,737 which issued July 9, 1985 to John I. Deckard; U.S. Pat. No. 4,550,875 which issued Nov. 5, 1985 to Richard F. Teerman, Russell H. Bosch, and Ricky C. Wirth; U.S. Pat. No. 4,603,671 which issued Aug. 5, 1986 to Turo Yoshinaga, et al.; U.S. Pat. No. 3,331,327 which issued to Vernon E. Roosa on Jul. 18, 1967; and U.S. Pat. No. 4,509,691 which issued Apr. 9, 1985 to Robert T. J. Skinner. An example of a high pressure common rail of the prior art may be found in U.S. Pat. No. 4,777,921, which issued Oct. 18, 1988, to Miyaki et al. Literature pertaining to electromagnetic fuel injection pumps may be found in Paper No. 880421 of the SAE Technical Paper Series entitled "EMI - Series - Electromagnetic Fuel Injection Pumps" discussed at the Feb. 29-Mar. 4, 1988 International Congress & Exposition at Detroit, Mich. Other literature pertaining to the subject include: SAE Technical Paper Series No. 840273 discussed Feb. 27-Mar. 2, 1984 at the International Congress & Exposition, Detroit, Mich.; SAE Technical Paper Series 850453 entitled "An Electronic Fuel Injection System for Diesel Engines" by P. E. Glikin discussed at the International Congress & Exposition at Detroit, Mich. on Feb. 25, 1985; SAE Technical Papers Series 810258 by R. K. Cross, P. Lacra, C. G. O'Neill entitled "Electronic Fuel Injection Equipment for Controlled Combustion in Diesel Engines," dated Feb. 23, 1981; SAE Technical Paper Series 861098 entitled "EEC IV--Full Authority Diesel Fuel Injection Control" by William Weseloh presented Aug. 4, 1986; and, United Kingdom Patent Application No. GB-2118624A filed Mar. 3, 1983 by Henry Edwin Woodward.